Combustion chamber with flameless oxidation

ABSTRACT

A combustion chamber ( 5 ) for a gas turbine is adapted for flameless oxidation of fuels. This circulation flow has an internal space ( 9 ) in which a large-volume circulation flow is established. To this end, the combustion chamber supplies a hot exhaust stream to the introduced air, the mass flow rate of which exceeds the fresh air stream. The fresh air and the fuel are fed to the combustion chamber in the same direction, roughly parallel to the wall.

FIELD OF THE INVENTION

The invention relates to a combustion chamber for a gas turbine and agas turbine equipped with such a combustion chamber.

BACKGROUND OF THE INVENTION

Gas turbines are used to convert heat energy to mechanical energy thatcan be delivered to a shaft (e.g., in a power plant, ship power plant,helicopter) or delivered as thrust (aircraft). All gas turbines havecombustion chambers in which a fuel is burned with excess air. Duringcombustion, a stable flame is formed in the combustion chamber. The gasflow, which has a very high velocity at the compressor outlet, isgenerally initially slowed for stabilization. Appropriate systems areprovided to form stable flames. For example, small eddies are generatedin the combustion chamber for flame stabilization. Combustion occurswith excess air so as not to cause thermal overload of the combustionchamber and turbine.

Flameless oxidation of a fuel in a corresponding reaction space is knownfrom EP 0463218 B 1. Flameless oxidation is achieved at high combustiontemperatures when the fuel is introduced to a gas stream containing hotexhaust and oxygen.

Combustion chambers of gas turbines have several design requirements.These include minimizing pressure loss, maximizing combustion, producing(just) under the maximum exhaust temperatures (to spare the turbine),and limited generation of NO_(x).

OBJECTS AND BRIEF SUMMARY OF THE INVENTION

In view of the foregoing, an object of the present invention isproviding a combustion chamber that has low NO_(x) generation and issuitable for use in gas turbines.

The combustion chamber according to the invention is configured forflameless oxidation. This is achieved by aligning the inlet and outletso that a large-volume recirculation flow is formed in the internalspace of the combustion chamber. As a result of this, larger amounts ofhot exhaust gases are mixed with the supplied fresh air. Preferably, theratios are preferably such that at least twice as much exhaust stream ismixed with the fresh air stream. Consequently, a situation can beachieved in which the mixture of fresh air and exhaust has a temperatureabove the ignition temperature of the fuel. The flameless oxidation thatdevelops does not rely on formation of a stable flame. Therefore,relatively high gas velocities can be used and the oxidation of the fuelextends over a larger zone between the inlet and outlet.

The large-volume recirculation flow can also be configured to berelatively low loss with the combustion chamber having low flowresistance and therefore causing only limited pressure losses. Pressurelosses of around less than 3% of the combustion chamber pressure areattainable. The fresh air is compressed and preferably fed to thecombustion chamber as an air jet without rotation. Ordered flow isproduced.

The new combustion chamber permits high power densities (for example 100MW/m³). Flame collapse and blowback are, in principle, impossible.NO_(x) concentrations of less than 10 ppm are achieved.

To form flameless oxidation while simultaneously achieving a combustionchamber with low flow resistance and a compact design, the fuel isintroduced to the combustion chamber in the same direction as the freshair. As a result, local eddies, which otherwise might contribute to anincrease in pressure loss, are largely reduced.

The combustion chamber is preferably laid out with an internalrecirculation of 2 to 5. This means that fresh air is mixed in with twoto five times as much exhaust gas.

The air and fuel are preferably introduced coaxially in adjacent jets orin jets otherwise arranged next and essentially parallel to each otherin the combustion chamber. The feed to the combustion chamber preferablyoccurs from the end wall in the area adjacent to the outer wall of thecombustion chamber, i.e., in a radially outward lying area of the endwall. As a result, fresh air and fuel are initially introduced into thecombustion chamber in flow essentially parallel to the wall. The outletof the combustion chamber is preferably oriented in the same or theopposite direction with the outer boundary of the outlet being closer tothe center axis of the combustion chamber than the air nozzles at theinlet into the combustion chamber. A recirculation stream of largervolume can be achieved with this expedient. The recirculation stream isguided along the wall from the inlet to the outlet of the combustionchamber, and then flows back from the outlet to the inlet, preferably onthe center axis of the combustion chamber.

The inlet of the combustion chamber is preferably formed by several airinlet nozzles that act as fresh air jets guiding fresh air into theinternal space. The air nozzles are also preferably formed so that theemerging air jet exerts an injector effect for return flow of exhaustgases. This can be achieved by a conical section protruding above theend wall of the combustion chamber.

The combustion chamber can be part of individual combustion chambersarranged in relation, which are also referred to as tubular combustionchambers. As an alternative, the combustion chamber can be laid out asan annular combustion chamber. In stationary installations alternativecombustion chamber shapes are also possible.

The combustion chamber is preferably designed so that it has only asingle circulation center (turbulence center). In the tubular combustionchamber this turbulence center is a line or surface arranged coaxial tothe longitudinal axis of the combustion chamber. The circulation streamis a toroidal stream that encompasses the entire internal space of thecombustion chamber. In the annular combustion chamber, in which the airnozzles belonging to the inlet are arranged, the turbulence center canalso formed on an outer rim in the end wall by a circular line alignedcoaxial to the longitudinal axis of the combustion chamber. Thiscircular line is preferably roughly parallel to the line along which theair nozzles are arranged.

The combustion chamber is preferably provided with a preheating devicefor bringing the combustion chamber to a temperature suitable forflameless oxidation at the start of operation. The preheating device isformed, for example, by temporarily operated burners that can form aflame by means of electric heating or other heat sources.

The combustion chamber can be coated on its inside wall with acatalytically active material. In addition, a guide element with acatalytic surface can be arranged in the combustion chamber. A catalystcan also be arranged at the outlet of the combustion chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a gas turbine according to theinvention.

FIG. 2 is a front view of the combustion chambers of the gas turbine ofFIG. 1.

FIG. 3 is a schematic longitudinal section view of an individualcombustion chamber.

FIG. 4 is a front view of the combustion chamber of FIG. 3.

FIG. 5 is a longitudinal section view of an alternative embodiment of acombustion chamber according to the present invention.

FIG. 6 is a longitudinal section view of another alternative embodimentof a combustion chamber according to the present invention.

FIG. 7 is a front view of an alternative embodiment of a combustionchamber according to the invention in which the combustion chamber isconfigured as an annular combustion chamber.

FIG. 8 is a longitudinal section view of the combustion chamber of FIG.7.

FIG. 9 is a longitudinal section view of an alternative embodiment of acombustion chamber according to the invention having reverse flow.

FIG. 10 is a front view of the combustion chamber of FIG. 9.

DETAILED DESCRIPTION OF THE INVENTION

A gas turbine 1 having a compressor 2, a turbine 3, which is connectedto the compressor 2 via a shaft 4, and at least one combustion chamber5, is shown in FIG. 1. Each combustion chamber has an inlet 6, which isfed compressed air from compressor 2, and an outlet 7, which suppliesthe gas stream generated in combustion chamber 5 to turbine 3.

As shown in FIG. 2, the combustion chambers 5 can be roughly can-typeburners which together form a combustion chamber set. A single suchcombustion chamber 5 is shown in FIG. 3. The combustion chamber has aninternal space 9 enclosed by a wall 8, which is essentially cylindrical.On the inlet side, an end wall 11, which can be flat, is part of thewall 8. On the opposite side, an end wall 12 is formed in which anopening 14 with radius B that defines the outlet 7 is arranged. A seriesof air nozzles 15 that, as shown in FIG. 4, are arranged in a circleserves as the inlet 6. The air nozzles 15 are arranged in the vicinityof the wall 8 at a radius A, greater than the radius B of opening 14,from the imaginary center axis 16 of the combustion chamber 5. In apractically tested embodiment, the diameter D of the nozzle opening ofthe air nozzles 15 is roughly {fraction (1/50)}^(th) the length 1 ofcombustion chamber 5 measured along center axis 16. The diameter of thecombustion chamber is about half its length. The figures are not toscale.

A guide tube 17 can be arranged in the internal space 9 concentric tothe center axis 16. The guide tube 17 is shorter than the length of theinternal space 9. This diameter corresponds to roughly the diameter ofthe opening 14. The guide tube is spaced from the end walls 11 and 12 adistance that is somewhat less than its radius. An arrangement forfastening the guide tube 17 to the wall 8 or end walls 11, 12 (e.g.bars) are not shown.

The air nozzles 15, as shown in FIG. 3, extend into the internal space9. For example, the air nozzles have a roughly truncated conicalcontour. The air nozzles are designed so that they produce a straightair jet that causes an injector effect. A fuel feed device 18 isprovided to supply fuel. This is formed, for example, by fuel nozzles 19that are fed by a central line 21. The fuel nozzles 19 can dischargeright in front of an air nozzle 15. One fuel nozzle 19 can then beassigned to each air nozzle 15. It is also possible to assign fuelnozzles 19 to only some of the air nozzles 15. In addition, the fuelnozzles 19 alternatively can be arranged between air nozzles 15, asshown in FIG. 4. The number of fuel nozzles 19 can match or differ fromthe number of air nozzles 15. The fuel nozzles 19 and the air nozzles 15have the same outflow direction, i.e., the air and fuel are introducedinto the internal space 9 in the same direction.

The combustion chamber 5 also has a preheating device 22 for startup. Inthe illustrated embodiment, the preheating device is formed by aspiral-wound filament that can be heated electrically and isaccommodated on the inside of wall 8. As an alternative, a burner, anarc generation device or another controllable heat source can beprovided.

The combustion chamber 5 thus described operates as follows:

During operation of the gas turbine 1, the combustion chamber 5 receivescompressed fresh air preheated by compression at its inlet 6. Forexample, the pressure can be in the range from 10 bar to 20 bar. The airis divided among the individual air nozzles 15 and therefore enters theinternal space 9 in the form of jets roughly parallel to the cylindricalwall 8. This is shown by arrows 24, 25 in FIG. 3. The temperature in theinternal space 9 is increased by the spiral-wound filaments 23 so thatthe introduced fuel is ignited. The fuel is fed fuel nozzles 19 alongwith the fresh air stream, into the internal space 9 in the direction ofarrows 24, 25. The fuel now reacts in this internal space on its wayfrom the air nozzles 15 to the end wall 12. The annular channel formedbetween the outside of the guide tube 17 and the inside of the wall 8therefore forms a reaction channel 26 that is traversed by the fresh airand fuel in the direction of arrows 27, 28.

The end of the reaction channel 26 is covered by end wall 12 so that theflow, which is indicated by arrows 29, 31 is reversed. Only a relativelysmaller portion of the formed reaction products flows via the outlet 7through the turbine 5 as hot gas, as shown by arrows 32, 33. Therelatively larger portion recirculates through the guide tube 17 back tothe end wall 11, therefore establishing a recirculation channel 34. Theexhaust flowing back in the recirculation channel 34 is at thecombustion chamber outlet temperature, for example 1300° C. The massflow rate is two to five times the feed flow rate of the air throughinlet 6.

The back-flowing gases are deflected radially on the end wall 11 anddrawn into the reaction channel 26 by the inflowing fresh air with aninjector effect. The hot exhaust mixes with the inflowing fresh air. Themixing temperature lies above the ignition temperature of the suppliedfuel, for example above 720° C. The fuel fed with the fresh airtherefore oxidizes completely, roughly along the length of the guidetube 17 within the reaction channel 26, without forming flame phenomena.No local temperature peaks develop within the gas volume.

After heating of the combustion chamber 8 and assumption of thedescribed stable flameless operation, the preheating device 22 can beswitched off. The flameless oxidation can be maintained in full andpartial load operation as long as it is ensured that the combustionchamber 8 is overall kept at a temperature above the ignitiontemperature of the fuel, and as long as the illustrated flow pattern ismaintained. The guide tube 17 here forms the areal turbulence center ofthe forming large-volume recirculation stream that has a tire-like ortoroidal shape. The turbulence center is therefore stably localized andis coaxial to the center axis 14.

In an alternative embodiment of the combustion chamber 5 shown in FIG.5, the circulation flow is achieved merely by arranging the air nozzles15 on the rim (such as shown in FIG. 4) and arranging of the openings14, and optionally by shaping of wall 8. The recirculation channel 34and reaction channel 26 in this case are not separated from each otherby fixtures, but are determined by the forming flow. The turbulencecenter of the recirculation flow is indicated with a dashed line in FIG.5 at 35. It lies concentric to the center axis 16.

In a further embodiment, a high temperature catalyst is arranged inoutlet 7. This serves for reaction acceleration, especially in the lowertemperature ranges.

Another embodiment of the combustion chamber 5 is shown in FIGS. 7 and8. This embodiment is designed as an annular combustion chamber. Wherereference numbers used thus far are employed, the previous descriptionapplies accordingly. The following explanations serve as a supplement.

The combustion chamber 5 is an annular internal space 9 arrangedconcentric to the longitudinal center axis 16 and enclosed by the wall 8both toward the center axis 16 and also outward. As shown in FIG. 8, thewall 8 can transition into the end walls 11, 12 with a curvature that isfavorable from the standpoint of flow. Air nozzles 15 that lie on acircle concentric to the center axis 16 are arranged in the end wall 11(FIG. 7). The flow direction established by air nozzles 15 isessentially parallel to the center axis 16. The end wall 12 can beprovided with an annular slit-opening 14 or instead with a series ofindividual openings 14 arranged on a rim. The outer rim, i.e., thelimitation 36 lying farthest outward radially, is arranged far enoughinward radially that the air jet emerging from air nozzle 15 strikes theend wall 12 radially farther out. In other words, as in the previousembodiments, the imaginary linear extension 37 of the air nozzle 15intersects the end wall 12 outboard of the opening 14. Accordingly, theflow emerging from the air nozzle 15 is diverted by 180° before theoutlet 7 and for the most part flows back to the end wall 11, where itis diverted again by 180°. A large circulating flow is formed that runsalong the entire length of the wall 8 of the combustion chamber 5. Theturbulence center 35 is arranged concentric to the center axis 16. Itpasses through the internal space 9 roughly in the center. As shown withthe dashed line, it can be established by a guide device 17′ or merelyby the shape of wall 8. As in the previous embodiments, flamelessoxidation occurs, with a complete reaction between the fuel and thesupplied fresh air on the way from the air nozzle to the end wall 12 sothat only waste gases are recirculated.

Another embodiment of the combustion chamber 5 according to theinvention is shown in FIGS. 9 and 10. The comments made relative to thecombustion chambers according to FIGS. 3 to 5 apply accordingly. Thefollowing applies in addition:

The combustion chamber 5 according to FIG. 9 operates with reverse flow.Whereas in the preceding combustion chambers, the inlet 6 and the outlet7 are arranged on opposite ends 11, 12 of combustion chamber 5, theinlet 6 and outlet 7 in combustion chamber 5 of FIG. 9 are arranged onthe same end 11 of combustion chamber 5. This design is suitable forturbines of relatively less power. It is typically applicable toturbines with radial compressors. The air nozzles 15 are arranged on acircle that encloses the opening 14 provided in end wall 11. The airnozzles 15 and the opening 14 are arranged concentric to the center axis16. The circulating flow that forms (arrows in FIG. 9) again has anannular circulation center 35 positioned concentric to the center axis16. The circulation flow has a mass flow rate that exceeds the mass flowrate of the supplied fresh air by a factor of two to five.

In comparison with the embodiments just described, the advantage of theFIGS. 9 and 10 embodiment of the combustion chamber 5 is that almost theentire internal space 9 is utilized as a reaction space. Both the pathfrom the air nozzle to the end wall 12 and the path from the end wall 12to the outlet 14 can be used for reaction of the fuel. As a result, avery compact design is possible.

If necessary, the circulation center 35 can be fixed or stabilized by aguide tube 17. In addition, the end wall 12 (shown with a dashed line inFIG. 9) can be curved as a torus, i.e., designed as a channel runningaround the center axis 16.

A combustion chamber 5 for a gas turbine is adapted for flamelessoxidation of fuels. To this end, the combustion chamber has an internalspace 9 in which a larger recirculation flow is established. Thisrecirculation flow feeds the introduced air to a hot exhaust streamwhose flow rate exceeds that of the fresh air stream. The fresh air andthe fuel are fed to the combustion chamber in the same direction,roughly parallel to the wall.

1. Combustion chamber (5) for a gas turbine (1) with an internal space(9) enclosed by a wall (8,11,12), which serves as a reaction space, withan inlet (6,15), which leads into internal space (9) and is suppliedwith fresh air, with at least one outlet (7,14), which emerges from theinternal space (9) and serves to discharge hot exhaust gases, in whichthe inlet (6,15) and the outlet (7,14) are aligned and the internalspace (9) is designed so that a large circulating flow is formed ininternal space (9) to maintain a flameless oxidation process with a fuelfeed device (18), set up to guide fuel into internal space (9) in astipulated direction (24), with the fuel feed device and inlet (6,15)being oriented essentially the same.
 2. Combustion chamber according toclaim 1, characterized by the fact that the cross sections of the inlet(6,15) and the outlet (7,14) and the geometry of the internal space (9)of the combustion chamber (5) are adjusted to each other so that themass flow rate of the gas stream circulating in the internal space islarger than twice the mass flow rate of the stream introduced into inlet(6,15).
 3. Combustion chamber according to claim 1, characterized by thefact that the cross sections of the inlet (6,15) and the outlet (7,14)and the geometry of the internal space (9) of the combustion chamber (5)are adjusted to each other so that the flow rate of the gas streamcirculating in the internal space is smaller than five times the flowrate of the stream introduced into inlet (6,15).
 4. Combustion chamberaccording to claim 1, characterized by the fact that the inlet (6,15)includes several air nozzles (15) arranged next to each other in a row.5. Combustion chamber according to claim 4, characterized by the factthat each air nozzle (15) has a section extending beyond wall (11). 6.Combustion chamber according to claim 4, characterized by the fact thatthe air nozzles (15) have a corresponding orientation.
 7. Combustionchamber according to claim 1, characterized by the fact that thecombustion chamber (5) is designed cylindrical and that the air nozzles(15) are arranged on a circle that is arranged concentric to combustionchamber (5).
 8. Combustion chamber according to claim 1, characterizedby the fact that the combustion chamber (5) is designed as a circularring.
 9. Combustion chamber according to claim 1, characterized by thefact that the inlet (6,15) and the outlet (7,14) are arranged, and thegeometry of the internal space (9) is established, so that the formingcirculation flow encompasses the entire internal space (9). 10.Combustion chamber according to claim 1, characterized by the fact thatthe recirculation flow has only a single turbulence center (35). 11.Combustion chamber according to claim 10, characterized by the fact thatthe turbulence center (35) lies on a curved line or a surface. 12.Combustion chamber according to claim 1, characterized by the fact thatthe combustion chamber (5) has a preheating device (22).
 13. Combustionchamber according to claim 1, characterized by the fact that a guidedevice (17) is arranged in internal space (9) that divides the internalspace (9) into a mixing and reaction channel (26) and a backflow channel(34).
 14. Gas turbine (1) with a compressor (2), a turbine (3) and withat least one combustion chamber (5) for flameless oxidation of fuel,enclosing an internal volume (9) and which has an inlet (6,15), whichestablishes an air inlet direction (24,25), that is connected tocompressor (2), an outlet (7,14) that is connected to turbine (3), and afuel feed device (18), which establishes a fuel introduction direction(24,25), characterized by the fact that the fuel introduction direction(24,25) and the air inlet direction (24,25) essentially agree.